Flexible conduit



July 6, 1965 D. R. PIERCE FLEXIBLE CONDUIT Filed May 2, 1962 I N VEN TOR. g/m/d X flak re mm J? j ATTQZX? United States Patent Ofi ice 3,192,795 Patented July 6, 1965 3,192,795 FLEXIBLE (IGNIIBUIT Donald R. Pierce, Ambler, P2,, assignor to Teleficx incorporated, North Wales, Pa, a corporation of Deiaware Filed May 2, 1962, er. No. $1,978 5 Qlairns. ({Ii. 74-501) The present invention relates to a flexible conduit assembly generally of the type in which a plastic tube is overlaid with a plurality of wires on a long lead and which wires are in turn overlaid with a protective covering. A core element is movably, i.e., rotatably, longitudinally or combinations thereof, supported within the inner tubular member.

More specifically, the present invention relates to a unique conduit construction in which a sheath is immediately overlaid upon an inner tube member and which sheath is a composite of metal and non-metal wire and filament elements laid on a long lead. Various combinations of said metal and non-metal elements are contemplated including the alternate circumferential spacing of such elements about the subadjacent tube.

Many important advantages are obtained with the subject type conduit. In the past, this type of conduit has been made with an essentially full com lement of long lead wires helically wrapped about the inner tubular member. Such a full complement does not necessarily mean that the adjacent long lead wires have been abutting and, in fact, in some instances such wires are definitely, even though slightly, spaced. However, such a full complement generallymeans that no more wires of the same diametral size can be added .to the wire sheath. Thus the expression sheath comprehends the disposition of such wires with at least a limited amount of circumferential space thcrebetween.

Wires are used in the normal sense in the present specification to mean metal wires.

Thus, in the present invention the replacement of some of the wires with lower cost non-metal elements, such as plastic filaments, results in important cost savings primarily due to the lesser material cost of such elements as compared to the replaced wires.

in at least one modification of the present invention one-half the normal comple ment of wires, e.g. 16, may be replaced with plastic filaments.

Another advantage of the subject conduit is the reduction in conduit weight due to the replacement of heavier metal wires with lighter non-metallic elements. This is an important advantage both in the reduced cost of shipping such conduit as well as the reduced installation weight thereof.

A still further and one of the most important advantages of the subject invention is that the flexibility of conduit made in accordance therewith is considerably enhanced as compared to previously made conduits utilizing all metal wire sheaths. This advantage is maximized when low frictional resistance plastic filaments, such as Teflon or nylon, are used on an alternating basis with the metal wires.

Where the subject invention is utilized with a flexible tubular member made of a plastic material, and further where an outer plastic cover is extruded over the conduit, the present invention has the important advantage that the replacement of some of the metal wires with nonmetal filaments permits better dimensional control of the plastic tube bore. In the previous types of all metal sheath conduits, the heat of extrusion of the plastic outer cover is readily conducted through the metal wires to the suhadjacent plastic tube which may actually cause the inner diameter of the plastic tube to be varied beyond terential sizing of the wire and filament elements;

desired tolerances.

vcovered with a plastic jacket or covering 13. bly includes a movable core element 20 disposed within The subject non-metal filament elements, e.g. nylon, are essentially non-conductive and, therefore, greatly reduce the transmission of the heat of extrusion of the outer plastic cover to the inner plastic tube. Thus, by greatly reducing the transfer of extrusion heat to the inner plastic tube, the dimensional stability of the conduit is considerably improved, with the result that the clearance between the inner plastic tube and the movable cable element may be maintained Within closer tolerances.

It is a general object of the present invention to provide a flexible inner tubular member of any suitable construction and material, which is overlaid with a plurality of wire members helically coiled on a long lead and at least periodically interspacing non-metallic filament elements circumferentialy intermediate adjacent of said wires.

The periodicity with which such filament elements are interspaced will be determined or varied in accordance with many factors including conduit loads, cost, weight,

flexibility desired, and criticality of heat transfer to an inner plastic tubular member.

In one modification of the present invention, a composite metal-plastic sheath includes alternate wire and filament elements helically wound about an inner plastic tubular member and which wires and filaments are of substantially the same diameter.

Another modification of the present invention also utilizes a composite metal-plastic sheath formed of alternate wires and filaments but in which the filament members and the wires are of distinctly different diameters. In such case either the wires or filaments may be larger.

For instance, if tension loads were not an important consideration, larger diameter plastic filaments and smaller diameter wires could be combined. Gn the other hand, where the loads to which the conduit is being subjected are relatively high, it might be preferred to make the wire members of a larger diameter than the plastic filaments. Other objects and advantages of the present invention will be apparent from a perusal of the detailed description which follows taken in conjunction with the drawings.

In the drawings: FIGURE 1 is a cut-away view of a flexible conduit embodying the subject invention;

FIGURE 2 is a view along line 22 of FIGURE 1; FIGURES 3 and 4' are modifications illustrating dif- FIGURE 5 is a further modification showing a limited number of filaments relative to the wires of the sheath.

"In the drawings like members are identified by the same numerals.

A flexible conduit assembly includes a conduit 10 comprising an inner tubular member 12 overlaid with a sheath 14, in turn, surrounded by roving 16 and finally The asseminner tubular member 12.

' Tubular member 12 may be formed in any satisfactory manner and of a suitable material so as to insure its flexibility and provide a low frictional support to permit core element 26 to be movable therewithin. While tubular member 12 may thus'assume many forms, it is preferred that such member be made of a plastic mate rial so as to provide a closed tube. While many plastic .materials may be utilized with the subject invention, highly desirable materials are the superpolyamide resins, commonly known as nylon and polytetrafluoroethylene also known Teflon.

jected, the helical sheath is generally wound with a rather long lead. Where compression loads become an important or significant factor, it is within the contemplation of the present invention that tubular member 12 may be formed magnitude of the loads to which the conduit is to be subor another element added to withstand such compression loads without making the conduit inflexible.

The most significant aspect of the subject invention is the manner in which sheath I4 is formed. Whereas in the past such sheath has been metallic due to the complete use of wire members, the subject invention utilizes a composite metal and non-metal sheath the details and variations of which will now be considered.

While other non-metallic materials, such as fiberglass, may be utilized in forming sheath 14, it is preferred to describe the invention as utilizing a plastic filament material such as nylon.

In the modification of FIGURES 1 and 2, a multiplicity of Wires 22 are helically laid about inner tubular member 12 on along lead. Adjacent wires 22 are circumferentially spaced whereby a plurality of plastic filament members 24 I may be similarly laid upon tubular member 12 intermediate adjacent wires 22. While both wires 22 and filaments 24 are laid firmly about tubular member 12, they are not bonded thereto, thus, limited movement of the wires and filaments relative to each other as well as to the subadjacent tubular member is contemplated to insure conduit flexibility.

In this modification, it is to be noted that wires 22 and filaments 24 are substantially of the same diameter. Also,

the wires and filaments may be circumferentially abutting without affecting the conduit flexibility. This is an extremely important feature of the combination of applicants composite metal and plastic sheath. In the past, where a full complement of metal wires was provided and further where such wires were in mutually abutting relation, such conduits had their flexibility greatly diminished. In other Words, to insure conduit flexibility it is necessary that there not only be relative movement between the wires and the subadjacent tubular member but also between the adiacent wires themselves. Where such wires are tightly packed and hence abutting, the frictional loads between the wires greatly diminishes the flexibility of a conduit. While conduits made in this manner can be bent, they frequently remain in the bent form and do not return to their normal straight configuration when the bending forces are relieved.

Prior to the present invention, the most preferred way of avoiding the aforesaid frictional loads occasioned by abutting wires has been to provide circumferential space between the sheath wires. Another Way of insuring flexibility where an abutting wire relationship is utilized is to make the sheath wires sufficiently stiff that they overcome the frictional loads between the wires and will thereby cause the conduit to flex back to an originally straight position. This latter alternative is generally undesirable due to the greater cost of the stifier wires as well as the considerable rigidity built into such conduit due to the wire stiffness. In preferred forms, the subject unique composite sheath construction takes advantage of the low frictional resistance of plastic filaments, made of materials such as nylon or Teflon, so that even though wires and filaments are abutting there is very low static or dynamic frictional resistance between the sheath members thereby assuring a highly flexible conduit.

Another distinct and important advantage of the conduit construction of FIGURES 1 and 2 is the greatly reduced weight thereof due to the substitution of lighter plastic filament members for the heavier wire members. In an average conduit constructed in accordance with the subject invention there could be as much as a 30% saving in wei ht as contrasted with a conduit using a full complement of wires.

The word filament is used broadly enough to comprehend an element that may be composed of a plurality of strands, or the like, woven or twisted to provide an element of the requisite size and strength. Fiberglass, if used, would undoubtedly be a multi-strand filament element.

. In the more preferred forms of the present invention, however, mono-filament plastic elements are utilized. Such mono-filament elements are easily extruded to the desired diametral size and, in general, have lower friction characteristics than stranded elements.

Two othervariations of the subject invention utilizing alternate wires and filaments to form a sheath about an inner tubular member are shown in FIGURES 3 and 4. Both of these variations illustrate the principle that the diametral sizes of the wires and filaments may be substantially different.

Referring to FIGURE 3, wire members 26 and filaments 28 are helically laid about an inner tubular member 12 with a relatively long lead. However, in this case Wires 25 are substantially larger than intermediate filaments 28. Filaments 28 are, however, sufficiently large as to maintain adjacent wires in a circumferentially spaced condition. In other words, filaments 28. are never so small as to permit circumferential engagement between adjacent wires 25.

The modification of FIGURE 3 might be utilized where the loads, generally tension, to which the conduit was to be subjected required the use of heavier wires or a greater number of such wires.

The modification of FIGURE 4 varies from that of FIGURE 3 in that the general size differential between the wires and filaments is reversed. In other words, in this case wires 36 are substantially smaller than filaments 32. This variation might be used where conduit loads are fairly light as a consequence of which a larger volume of plastic filament relative to wires maybe used resulting in a lighter weight, less expensive, and more flexible conduit.

A still further variation of the subject invention is shown in FIGURE 5. In this case instead of interposing a plastic filament between each wire 34, as few as one or two filaments may be utilized. In this instance, the sheath comprises a plurality of helically wound wires 34 on a long lead with a pair of plastic filament members 36 selectively interposed. While the wires thereadjaccnt may abut filaments 36, the remainder of wires 34 are slightly circumferentially spaced with respect to each other to eliminate abutting frictional loading.

As a corollary to the modification shown in FIGURE 5, it is contemplated that a sheath may be constructed in which a larger number of non-metal or plastic filaments relative to wires may be used to provide a full complement sheath.

The periodicity with which the filaments are interspaced between the wires may be varied. from the alternating variations of FIGURES 1 through 4- to the more limited number illustrated in FIGURE 5. The particular construction desired will depend primarily on the use to be made of the conduit. In general, the more filaments used, the lighter, less expensive, more flexible and less heat conductive will be the composite metal plastic sheath.

The feature of the subject composite metal-plastic sheath being less heat conductive is particularly significant and advantageous with a conduit of the type illustrated in FIGURE 1 in which a substantial number of such filaments are utilized. As noted, an important problem in manufacturing with conduits utilizing inner plastic tubular members is in the maintaining the latters inside diamet r so as to insure a smoothly operating core element and at the same time insuring against too much clearance between the core element and the tube. A part of the problem of maintaining plastic tube 1.1). within tolerances has been in the actual manufacture of the plastic tubing. On the other hand, even where such tubing is manufactured within prescribtd tolerances, the inner tubular member may be subjected to sufficient heat during the formation of the conduit to disrupt these tolerances. For instance, outer covering 18 is normally extruded over the sheath 14. Inevitably the plastic is extruded in a hot condition. Even though the conduit may be subsequently quenched or cooled in a water tank, with an all metal sheath a good bit of this heat may be conveyed to the inner tubular member and thereby disrupt the previously maintained tolerances.

On the other hand, the present invention which utilizes a composite meta -plastic sheath reduces by as much as one-half the amount of sheath metal through which heat can be conducted. The combination, therefore, greatly reduces the transfer of heat to the inner plastic tubular member 12 during the extrusion of cover 13. In this way, it is considerably easier to maintain the tolerances, and particularly the I.D., of the inner tubular member.

The closer maintenance of the plastic tube I.D. within prescribed limits results in a higher quality conduit particularly Where backlash and/ or friction between tube and core element are important operating considerations.

Applicant is well aware of flexible all-metal sheath conduits utilizing a plurality of long lay wires in which thread or cord members have been disposed between the wires. Such fiber members have nothing to do with the present invention and, as shown and described in Patent 1,896,285 Burd, have merely been used in an eflort to prevent grease from oozing out between the wires.

To applicants knowledge, he is the first to form such a flexible conduit with .a composite metal wire and plastic or non-metal filament sheath. More specifically, applicant is apparently the first to use non-metal filaments to space such wire members with the attendant advantages of lower conduit cost, weight and greater flexibility.

It is apparent that various other modifications may be made in the subject conduit within the intended scope of the invention as set forth in the hereinafter appended claims.

I claim:

1. A flexible conduit assembly comprising a tubular member, a multiplicity of wires wrapped helically about said tubular member with a long lead, adjacent of said wires being circumferentially spaced from each other, a plurality of low frictional resistance plastic elements helically wrapped about said tubular member with a long lead and disposed within the spaces between adjacent wires, said elements being of suflicient diametral size to maintain adjacent of said wires in a non-abutting relationship, and a flexible core element movably supported within said tubular member.

2. A flexible conduit assembly comprising a tubular member, a multiplicity of wires wrapped helically about said tubular member with a long lead, adjacent of said wires being circumferentially spaced from each other, a plurality of low frictional resistance plastic elements helically wrapped about said tubular member with a long lead and disposed within the spaces between adjacent wires, said elements being of sufficient diametral size to maintain adjacent of said wires in a non-abutting relationship, an extruded plastic casing enclosing said wires and plastic elements, and a flexible core element movably supported within said tubular member.

3. A flexible conduit assembly comprising a plastic tubular member, a multiplicity of wires wrapped helically about said member with a long lead, adjacent of said wires being circumferentially spaced from each other, a plurality of low frictional resistance plastic filament elements helically wrapped about said tubular member and being disposed within the spaces between adjacent of said wires, said elements being substantially the same diametr-al size as said wires, an extruded plastic casing enclosing said wires and said elements, and a flexible core element movably supported within said tubular member.

4. A flexible conduit assembly comprising .a plastic tubular member, a multiplicity of wires wrapped helically about said member with a long lead, adjacent of said wires being circumferentially spaced from each other, a plurality of low frictional resistance plastic mono-filament elements helically wrapped about and abuttingly engaging said tubular member, said mono-filament elements being disposed within at least some of the spaces between adjacent of said wires, said wires and elements coacting to form a composite metal and plastic sheath about said tubular member, and a flexible core element movably supported within said tubular member.

5. A flexible conduit assembly comprising a plastic tubular member, a multiplicity of steel wires wrapped helically about said member with a long lead, a multiplicity of nylon filament elements helically wrapped about said tubular member with a long lead and circumferentially interspaced between said wires whereby said wires and filament elements coact to form a composite metal and nylon sheath about said tubular member, an extruded plastic casing enclosing said composite sheath, and a flexible core element movably supported within said tubular member.

References Cited by the Examiner UNITED STATES PATENTS 1,205,984 11/16 Forsyth 138-133 1,697,541 1/29' Schurer 174--l08 2,7 06,494 4/55 Morse. 2,821,092 1/58 Cordora et a1. 2,850,915 9/58 Bratz. 3,013,443 12/61 Morse. 3,015,969 1/ 62 Bratz 64----2 BROUGHTON G. DURHAM, Primary Examiner.

KARL J. ALBRECHT, ROBERT C. RIORDON,

FRANK SUSKO, Examiners. 

1. A FLEXIBLE CONDUIT ASSEMBLY COMPRISING A TUBULAR MEMBER, A MULTIPLICITY OF WIRES WRAPPED HELICALLY ABOUT SAID TUBULAR MEMBER WITH A LONG LEAD, ADJACENT OF SAID WIRES BEING CIRCUMFERENTIALLY SPACED FROM EACH OTHER, A PLURALITY OF LOW FRICTIONAL RESISTANCE PLASTIC ELEMENTS HELICALLY WRAPPED ABOUT SAID TUBULAR MEMBER WITH A LONG LEAD AND DISPOSED WITHIN THE SPACES BETWEEN ADJACENT WIRES, SAID ELEMENTS BEING OF SUFFICIENT DIAMETRAL SIZE TO MAINTAIN ADJACENT OF SAID WIRES IN A NON-ABUTTING RELATIONSHIP , AND A FLEXIBLE CORE ELEMENT MOVABLY SUPPORTED WITHIN SAID TUBULAR MEMBER. 